The present invention relates to a novel press-contact connector for electrical connection between circuit boards in a compact-size electronic instrument including, typically, mobile phones or, in particular, for electrical connection between the electrode terminals on a fixed circuit board and the electrode terminals on a flexible circuit board of the TAB (tape-automatic bonding) type as well as to a method for the preparation of the connector.
As is known, press-contact connectors are classified into several types including rubber connectors, metal filament connectors, metal-filament matrix connectors and U-formed metal filament connectors. These different types of connectors are each required to have adaptability to compensation for mounting errors and low conduction resistance. The above mentioned rubber connector has a structure formed from an alternation of electroconductive and insulating layers each of a rubbery material such as a silicone rubber. Such a rubber connector is prepared by slicing a rubber block having an alternately stratified structure of two types of rubber sheets in a plane in the direction of stratification and slitting the slices into connector strips. The metal filament connector is prepared by slitting an integral body of two insulating rubber sheets sandwiching an array of metal filaments aligned in an arrangement at a uniform pitch into strips in a direction perpendicular to the running direction of the metal filaments.
The metal-filament matrix connector is prepared by slicing an alternately laminated block of insulating rubber layers and arrays of metal filaments running in one and the same direction and each sandwiched between two adjacent rubber layers in a direction perpendicular to the plane of the rubber sheets into slices which are each slitted in a suitable width. The U-formed metal filament connector is prepared by arranging a plurality of metal filaments in parallel each to the others on the surface of an insulating rubber sheet at a regular pitch to form a metal filament-bearing sheet which is introduced into and molded in the cavity of a metal mold having a U-formed cross section followed by filling of the cavity with an insulating rubber so that the connector has a plurality of metal filaments exposed on the outer surface of the insulating rubber body.
The press-contact connectors are used in recent years, besides the use for electrical connection between an LSI and a printed circuit board or between two printed circuit boards, for electrical connection between circuit boards in a compact-size intercommunication instrument represented by mobile phones or, to say more particularly, between a set of electrode terminals on a fixed circuit board and a set of electrode terminals on a flexible circuit board of TAB. It is very important for the press-contact connector in such an application that electrical connection through the connector between the sets of electrode terminals is complete even with a very small contacting pressure since otherwise warping or twisting deformation may occur in the casing or circuit boards of the compact-size intercommunication instrument which is so compact and light-weighted as not to withstand a large contacting pressure.
The press-contact connectors of the above described types each have several problems when used for electrical connection between circuit boards in a very compact intercommunication instrument. In the rubber connectors, for example, troubles are sometimes encountered due to delay or loss of transmission of digital signals as a consequence of the relatively large electric resistance of the conductive rubber layers so that rubber connectors cannot be used for connection between circuit boards in a compact-size intercommunication instrument in view of a possible failure in the performance of the instrument.
Each of the press-contact connectors of the other types utilizing metal filaments as the conductive body is not absolutely unsuitable for electrical connection between circuit boards in a compact-size intercommunication instrument because the contacting pressure can be so reduced when the metal filaments each take a slanted disposition or a bent or curved form. The contacting pressure ultimately required in the connectors of these types, however, depends on the hardness of the rubber as the material of the matrix and the size of the connector per se or, namely, the contacting area so that the above mentioned slanted disposition or bent or curved form of the metal filaments alone is not always sufficient to fully ensure a low contacting pressure for electrical connection.
As a means to solve the above described problems, it would be a due idea to use a rubber of decreased rubber hardness, to have a decreased contacting area or to increase the amount of compression. A rubber material of a low rubber hardness, however, has other problems of an increase in the permanent compression set and an increased rate of thermal denaturation or elastic fatigue. The contacting area of a press-contact connector cannot be decreased to be small enough and a serious disadvantage of poor handling adaptability is resulted by the use of a press-contact connector with an excessively small contacting area. When the amount of compression in the press-contact connector is decreased, the error in mounting can no longer be absorbed resulting in failure of electrical connection through the connector.
A conclusion derived from the above consideration is that absorption of mounting errors under a condition of a decreased contacting load can be accomplished only by the use of an auxiliary member such as a rubber plate or rubber tube having an open space available for decreasing the contacting area. Serious problems accompanying the use of such an auxiliary member are that the connection height is necessarily increased so much and that the number of the parts forming the instrument is necessarily increased so many.